A Method for Interfacial Enhancement and Insulation Modification of Two-Component Liquid Silicone Rubber Cable Accessories

Abstract

The present invention discloses a method for interfacial enhanced insulation modification of two-component liquid silicone rubber cable accessories, belonging to the technical field of electrical engineering materials. The present invention solves the technical problem that the interfacial enhanced insulation modification of existing two-component liquid silicone rubber cable accessories cannot balance electrical properties and mechanical properties. The present invention provides a method for high-quality and high-efficiency surface modification of enhanced insulation of two-component liquid silicone rubber cable accessories. Without introducing crosslinking agents and crosslinking aids, grafting of small molecules on the surface of the molded silicone rubber enhanced insulation is completed, which can not only achieve controllable surface grafting density and grafting depth, improve the interfacial breakdown performance, but also balance the improvement of its mechanical properties.

Description

Technical Field

[0001] The invention relates to a method for improving the insulation of a two-component liquid silicone rubber cable accessory interface, and belongs to the technical field of electrical materials. Background Art

[0002] Cable accessories are used to connect cables to cables or cables to power systems. They are mainly divided into three categories: prefabricated cable accessories, wrapped cable accessories and molded cable accessories. Prefabricated cable accessories are mainly divided into two categories: prefabricated cable terminals and prefabricated cable intermediate joints. Different from wrapped cable accessories and molded cable accessories, the reinforced insulation of prefabricated cable accessories is pre-processed and manufactured in the cable accessories production workshop, so its processing precision is high, avoiding the quality problems caused by manufacturing wrapped or molded reinforced insulation at the installation site. Prefabricated cable accessories have many advantages such as high quality controllability, simple installation process and short installation cycle. Therefore, they are almost an inevitable choice in high-voltage cross-linked polyethylene insulated power cable lines with voltage levels of 35kV and above.

[0003] There is only radial electric field distribution in the cable insulation layer, and there is no axial electric field along the laying direction of the cable core. However, in the cable accessories, the regularity and continuity of the outer shielding structure are destroyed, so the electric field is seriously distorted, and there are not only radial electric fields but also axial electric fields. Therefore, the electric field distribution in high-voltage cable accessories is the most concentrated part of the cable system insulation structure, and it is also the weakest link in the cable system. The radial electric field usually causes penetrating internal damage in the cable body insulation or reinforced insulation, while the existence of the axial electric field will cause partial discharge or flashover breakdown along the interface direction at the interface between the reinforced insulation made of rubber material and the cable body insulation made of cross-linked polyethylene.

[0004] The structure of the stress control body of prefabricated cable accessories mainly includes two parts: semi-conductive stress cone and reinforced insulation, and is mostly made of silicone rubber material. Improving the electrical resistance of prefabricated cable accessories rubber reinforced insulation materials can effectively improve the working reliability of cable accessories. In order to enhance the electrical properties of insulating rubber materials, the existing technology mainly modifies the rubber material by adding nanoparticles. One is to improve the nonlinearity of the electrical conductivity of rubber through nanoparticles, thereby improving the electric field distribution of the stress control body, so that the electric field in the stress control body is much lower than the breakdown strength of the material, ensuring stable operation; the other is to improve the breakdown strength or resistance to electrical treeing of the rubber material by adding nanoparticles.

[0005] In order to improve the interface insulation performance of the stress control body, the existing technology usually applies a layer of insulating silicone grease between the rubber stress control body and the cable body insulation to reduce the resistance of the stress control body installation process and improve the electrical resistance of the insulation interface. However, the silicone grease is easy to be lost or cause the rubber material to swell during long-term operation, and it is impossible to effectively maintain the interface electrical resistance for a long time.

[0006] In addition, the prior art proposes a surface grafting treatment method for the stress control body of cable accessories that can achieve long-lasting and effective modification. The surface grafting scheme in this technology is to modify the surface of the enhanced insulation by chemical grafting of a graftable aromatic ketone compound under heat treatment or ultraviolet irradiation conditions with the participation of a crosslinking agent and a crosslinking aid after the stress control body has been processed and vulcanized. However, there are two problems in the application of this prior art:

[0007] 1. This method lacks high efficiency, because this method essentially introduces a new reaction system into the surface layer of the reinforced insulation. When the rubber reinforced insulation has been vulcanized, excessive use of initiators and cross-linking agents will not only increase the modification cost, increase the production steps, and reduce the production efficiency, but also easily cause adverse effects on the performance of the reinforced insulation material.

[0008] 2. This method lacks specificity. The same treatment method is used for EPDM rubber and silicone rubber in this technical solution, but there is a lack of specific design for two-component liquid silicone rubber insulation materials for high-voltage cable accessories. There are many types of silicone rubber, which can be divided into more than a dozen categories such as liquid silicone rubber and mixed silicone rubber according to the vulcanization reaction principle and processing technology. Among them, high-temperature vulcanization addition type two-component liquid silicone rubber has good fluidity, processing performance and vulcanization performance, and is particularly suitable for making reinforced insulation and stress cone structures for cable accessories with complex structures and high dimensional accuracy requirements. However, the mechanical properties of this type of rubber are relatively poor, and the tear strength is low. When it is surface-modified using initiators, co-crosslinking agents and irradiation, not only is the grafting efficiency low, but it also damages its mechanical properties, which leads to limited improvement in the working reliability of cable accessories, and it is reduced due to mechanical aging.

[0009] That is to say, for stress control bodies made of two-component liquid silicone rubber materials, when enhancing interface insulation, we should not only focus on their electrical properties, but also pay more attention to the changes in their mechanical properties before and after grafting modification, and design more efficient and less damaging grafting modification methods to strictly prevent the limited mechanical properties from being damaged. Therefore, it is very necessary to provide a method for interface insulation enhancement modification of two-component liquid silicone rubber cable accessories. Summary of the invention

[0010] In view of the technical problem that the existing interfacial enhanced insulation modification of two-component liquid silicone rubber cable accessories cannot take into account both electrical properties and mechanical properties, the present invention provides a method for interfacial enhanced insulation modification of two-component liquid silicone rubber cable accessories.

[0011] The technical solution of the present invention:

[0012] One of the objectives of the present invention is to provide a method for modifying the interface enhanced insulation of two-component liquid silicone rubber cable accessories, and the method includes the following steps:

[0013] (1) Preform two-component liquid silicone rubber to obtain a preformed cable accessory sample;

[0014] (2) Spray the heat-melted graftable compound on the surface of the cable accessory sample, and at a temperature above the melting point of the graftable compound, use a mold to apply pressure to this surface to make the graftable compound form a uniform liquid film. After continuously applying pressure for a certain time, perform a vulcanization grafting treatment on the whole;

[0015] (3) After the vulcanization treatment is completed, remove the mold, rinse the modified surface with a solvent, and dry it to complete the interfacial insulation modification of the two-component liquid silicone rubber cable accessory.

[0016] Further defined, the operation process of (1) is: fully mix component A and component B that make up the two-component liquid silicone rubber, inject them into the mold of the cable accessory, and perform pressure heating treatment to obtain a preformed two-component liquid silicone rubber cable accessory sample.

[0017] Further defined, component A includes vinyl raw rubber and a platinum catalyst; component B includes vinyl raw rubber and hydrogen-containing silicone oil.

[0018] Even further defined, inorganic nanoparticles are also included in component A and component B.

[0019] Further defined, the pressure heating treatment conditions are: temperature 90 - 120 °C, pressure 10 - 15 MPa, and time 8 - 15 min.

[0020] Further defined, the graftable compound in (2) is a small molecule compound capped with a vinyl unsaturated group whose melting point is not higher than 200 °C, boiling point is not lower than 200 °C, and the temperature corresponding to the peak value of the differential thermogravimetric curve is not lower than 200 °C.

[0021] Even further defined, the graftable compound is 4-propenyloxy-2-hydroxybenzophenone.

[0022] Further defined, the pressure application time of the mold to the sample surface in (2) is 10 - 60 min, and the pressure is 300 - 600 Pa.

[0023] Further limitation: in (2), the vulcanization grafting treatment temperature is 180 - 220 °C, and the time is 3 - 8 h.

[0024] Further limitation: in (2), the spraying amount of the graftable compound is 1 - 2 g / dm 2 .

[0025] Further limitation: in (2), the mold is made of inorganic glass or ceramic material.

[0026] Further limitation: in (3), the solvent is acetone.

[0027] Beneficial effects:

[0028] The present invention provides a method for enhancing insulation and high-quality and high-efficiency surface modification of two-component liquid silicone rubber cable accessories. Without introducing cross-linking agents and cross-linking aids, grafting of small molecules on the surface of the molded silicone rubber enhanced insulation is completed. It can not only achieve controllable surface grafting density and grafting depth, improve the interface breakdown performance, but also take into account the improvement of its mechanical properties. Compared with the prior art, it has the following advantages:

[0029] (1) The present invention improves the surface characteristics of two-component liquid silicone rubber materials by means of surface chemical grafting. Compared with the commonly used methods such as applying insulating silicone grease in the prior cable accessory technology, there is no risk of molecular loss after grafting, nor is there a risk of causing rubber swelling, and it has long-term reliable stability;

[0030] (2) In the grafting modification scheme adopted by the present invention, cross-linking agents and cross-linking reaction aids and other components are not used. Instead, the vulcanization reaction system of the two-component addition-cured liquid silicone rubber itself is effectively utilized to achieve surface grafting of small molecules. It not only overcomes the negative impact of introducing new grafting reaction systems and additive components on the modification effect, but also greatly reduces the modification economic cost and simplifies many process steps such as the preparation of multi-component solutions, and has the characteristics of economy and high efficiency;

[0031] (3) Based on the vulcanization reaction principle and processing and forming characteristics of the high-temperature vulcanization addition-cured two-component liquid silicone rubber of the present invention, by controlling the temperature and time of pre-forming the sample, pre-forming is completed at an appropriate degree of cross-linking, which not only maintains the shape stability of the sample, but also reserves sufficient chemical reaction sites for the subsequent small molecule grafting reaction, and can be coordinated and adjusted by process parameters such as temperature, pressure, and time to control the grafting density and grafting depth of surface grafting, so as to improve the interface electrical performance of the stress control body. At the same time, since there is no additional cross-linking agent, additive, irradiation, etc. involved in the grafting process, and no new grafting reaction system is introduced, a beneficial effect different from other surface chemical grafting methods is produced, so that the mechanical properties of the grafted material are not only not lost, but are instead improved to a certain extent, and it has the characteristics of no negative effect and high modification quality. Brief Description of the Drawings

[0032] Figure 1 It is the schematic diagram of the graft reaction principle for the interfacial enhanced insulation modification of the two-component liquid silicone rubber cable accessory of the present invention;

[0033] Figure 2 It is the comparative infrared absorption spectrum diagram of the interfaces of the specimens prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0034] Figure 3 It is the schematic diagram of the surface breakdown test electrode and the specimen structure;

[0035] Figure 4 It is the schematic diagram of the tensile test specimen specifications;

[0036] Figure 5 It is the comparative infrared absorption spectrum diagram of the interfaces of the specimens prepared in Comparative Example 3 and Comparative Example 1. Detailed Embodiments

[0037] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the embodiments of the specification.

[0038] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0039] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0040] Example 1

[0041] (1) After thoroughly mixing the addition-type two-component liquid silicone rubber A component and B component under vacuum, they are filled into a 100*100 mm mold. The thickness of the mold depends on different experimental requirements. After filling into the mold, vacuum is drawn to remove the residual micropores inside, and then it is processed at a temperature of 110°C and a pressure of 15 MPa for 10 minutes to complete the pre-forming of the specimen, obtaining a pre-formed specimen;

[0042] (2) selecting 4-propyleneoxy-2-hydroxybenzophenone as a graftable compound, the compound having a vinyl end group, a melting point of (67-70° C.), a boiling point greater than 400° C., a thermal weight loss peak temperature greater than 200° C., heating at 80° C. to completely melt it, and obtaining a liquid graftable compound;

[0043] (3) In an oven at 80°C, 1.5 g of the liquid graftable compound is evenly coated on the front of the preformed sample, and then the sample is clamped between two smooth inorganic glass molds, placed horizontally, and a 500 g weight is pressed on the upper part of the mold. Under the pressure of the mold, the liquid forms a uniform liquid film, which is further kept evenly covered on the surface of the sample, and the surface is continuously absorbed at 80°C for 30 min;

[0044] (4) Maintaining the surface pressure, transfer the weight, glass cover and sample as a whole to a 200°C electric heating blower for 4 hours to complete the vulcanization and surface grafting treatment at the same time;

[0045] (5) The grafted sample was ultrasonically cleaned with acetone solvent and placed in a vacuum oven at 80° C. for 48 h to complete the interface insulation modification of the two-component liquid silicone rubber.

[0046] The grafting reaction principle of the two-component liquid silicone rubber interface insulation modification in this embodiment is as follows Figure 1 As shown by Figure 1 It can be seen that the present invention improves the surface properties of the two-component liquid silicone rubber material by surface chemical grafting, effectively utilizing the vulcanization reaction system of the two-component addition liquid silicone rubber itself to achieve surface grafting of small molecules, and no new grafting reaction system is introduced in the reaction process.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that no grafting modification is performed. The specific operation process is as follows:

[0049] (1) After the addition type two-component liquid silicone rubber component A and component B are fully mixed under vacuum, they are filled into a 100*100 mm mold. The mold thickness depends on the experimental requirements. After filling the mold, vacuum is drawn to remove the residual micropores inside. Then, the sample is preformed at 110°C and 15MPa for 10 minutes to obtain a preformed sample;

[0050] (2) The preformed sample was transferred to an electric heating bellows at 200°C for 4 hours to complete the vulcanization treatment and obtain an ungrafted two-component liquid silicone rubber.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 1 is that the preforming temperature in (1) is 130°C, and the other process steps and parameter settings are the same as those in Example 1. The specific operation process is as follows:

[0053] (1) After the addition type two-component liquid silicone rubber component A and component B are fully mixed under vacuum, they are filled into a 100*100 mm mold. The mold thickness depends on the experimental requirements. After filling the mold, vacuum is drawn to remove the residual micropores inside. Then, the sample is preformed at 130°C and 15MPa for 10 minutes to obtain a preformed sample;

[0054] (2) selecting 4-propyleneoxy-2-hydroxybenzophenone as a graftable compound, the compound having a vinyl end group, a melting point of (67-70° C.), a boiling point greater than 400° C., a thermal weight loss peak temperature greater than 200° C., heating at 80° C. to completely melt it, and obtaining a liquid graftable compound;

[0055] (3) In an oven at 80°C, 1.5 g of the liquid graftable compound is evenly coated on the front of the preformed sample, and then the sample is clamped between two smooth inorganic glass molds, placed horizontally, and a 500 g weight is pressed on the upper part of the mold. Under the pressure of the mold, the liquid forms a uniform liquid film, which is further kept evenly covered on the surface of the sample, and the surface is continuously absorbed at 80°C for 30 min;

[0056] (4) Maintaining the surface pressure, transfer the weight, glass cover and sample as a whole to a 200°C electric heating blower for 4 hours to complete the vulcanization and surface grafting treatment at the same time;

[0057] (5) The grafted sample was ultrasonically cleaned with acetone solvent and placed in a vacuum oven at 80° C. for 48 h to complete the interface insulation modification of the two-component liquid silicone rubber.

[0058] Comparative Example 3

[0059] The difference between this comparative example and Example 1 is that dicumyl peroxide is used to replace part of 0.75g of 4-propyleneoxy-2-hydroxybenzophenone, and the remaining process steps and parameter settings are the same as those in Example 1. The specific operation process is as follows:

[0060] (1) After the addition type two-component liquid silicone rubber component A and component B are fully mixed under vacuum, they are filled into a 100*100mm mold. The mold thickness depends on the experimental requirements. After filling the mold, vacuum is evacuated to remove the residual micropores inside. Then, the mold is treated at 120°C and 15MPa for 10 minutes to complete the primary vulcanization and press molding. Then, it is directly transferred to a 200°C electric heating blower for 4 hours to complete the secondary vulcanization.

[0061] (2) Put 0.75 g of 4 - allyloxy - 2 - hydroxybenzophenone and 0.75 g of dicumyl peroxide powder into a beaker, stir evenly, place it in an oven and heat to 80 °C for 30 min. After the powder is completely melted, stir with a glass rod for 10 min to obtain an organic modified solution;

[0062] (3) Use a silicone rubber brush to evenly apply the obtained organic modified solution on the front of the above - obtained specimen. Place the specimen in an oven at 80 °C. After maintaining a constant temperature for 15 min, raise the oven temperature to 145 °C and continue to maintain it for 30 min to fully decompose dicumyl peroxide into free radicals, and initiate the grafting reaction of 4 - allyloxy - 2 - hydroxybenzophenone on the surface of the silicone rubber under the action of free radicals;

[0063] (4) Take the grafted specimen, perform ultrasonic cleaning on it with acetone solvent, and place it in a vacuum oven at 80 °C for 48 h to complete the interfacial insulation modification of the two - component liquid silicone rubber.

[0064] Effect example

[0065] (1) Perform infrared absorption spectroscopy characterization on the specimens prepared in Example 1, Comparative Example 1, and Comparative Example 2. The results are as Figure 2 shown. It can be seen from Figure 2 that there are significant differences between the infrared absorption spectra of the modified specimens in Example 1 and the unmodified silicone rubber specimens in Comparative Example 1. In the infrared absorption spectrum of the modified specimens, significant benzene ring and carbonyl absorption peaks of 4 - allyloxy - 2 - hydroxybenzophenone small molecules appear. The above phenomena indicate that 4 - allyloxy - 2 - hydroxybenzophenone molecules have been successfully grafted on the material surface. However, no obvious benzene ring and carbonyl absorption peaks of 4 - allyloxy - 2 - hydroxybenzophenone small molecules appear in the infrared absorption spectrum of the specimens obtained in Comparative Example 2, which shows that the pre - forming temperature has a significant impact on the grafting efficiency.

[0066] (2) Paste two pieces of aluminum foil in the shape shown in the appendix on the front of the specimens prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively, as the high - voltage electrode and the grounding electrode for the surface withstand voltage test. Among them, the triangular electrode is used as the high - voltage electrode, and the rectangular electrode is used as the grounding electrode. The minimum distance between the two electrodes is 2 mm. Apply a uniformly increasing DC high voltage to the high - voltage electrode until surface flashover occurs in the nearest area between the two electrodes on the surface of the specimen. Test and record the surface flashover voltages of 10 specimens respectively. The test results are statistically analyzed by the two - parameter Weibull distribution function, and the results are shown in Table 1 below: Figure 3

[0067] Table 1

[0068] Eigenvalue of surface breakdown voltage kV Shape parameter Example 1 10.47 5.31 Comparative Example 1 4.57 7.29 Comparative Example 2 4.97 6.83

[0069] ​As can be seen from Table 1, the interfacial breakdown voltage of Example 1 is increased by 129% compared with that of Comparative Example 1. At the same time, the interfacial breakdown voltage of Comparative Example 1 is only increased by 8.7% compared with that of Comparative Example 2, indicating that the grafting efficiency in the present invention is the key parameter affecting the surface flashover voltage. Given that too low preforming temperature will lead to too long required reaction time, if the reaction time is controlled unchanged, the preforming of the specimen will fail and secondary processing cannot be carried out. Taking temperature and time as experimental factors and the test results of infrared absorption spectrum and the improvement effect of surface flashover as experimental indicators, through a series of experiments, the reaction temperature condition is finally selected as 90 - 120 °C and the reaction time is 8 - 15 min to ensure the high efficiency of grafting to the greatest extent.

[0070] (3) According to the parameter requirements given in GB / T528 - 2009 (Determination of tensile stress - strain properties of vulcanized rubber or thermoplastic rubber), the specimens obtained in Example 1 and Comparative Example 1 were cut into dumbbell - shaped specimens with a thickness of 1 mm using a cutter. The specimen dimensions are as Figure 4 shown, the clamp spacing is 20 mm, and the tensile rate is 500 mm / min. The tensile strength of the specimen in Comparative Example 1 was measured to be 5.84 MPa, and the elongation at break was 457.8%. The tensile strength of the specimen in Example 1 was 6.43 MPa, and the elongation at break was 520.7%. By comparison, it can be seen that the tensile strength of Example 1 is increased by 10.1% compared with that of Comparative Example 1, and the elongation at break is increased by 13.7%, indicating that the grafting method provided by the present invention has the advantages of high quality and no negative effects.

[0071] (4) Infrared absorption spectrum test was carried out on the modified specimen of Comparative Example 3 and compared with the specimen of Comparative Example 1 without grafting modification. The results are as Figure 5 shown. The infrared absorption spectrum diagram of the modified specimen of Comparative Example 3 is exactly the same as that of the unmodified silicone rubber specimen of Comparative Example 1, and no absorption peaks of small - molecule benzene rings and carbonyl groups appear. This phenomenon indicates that the 4 - acryloxy - 2 - hydroxybenzophenone small molecules cannot be grafted onto the material surface or the grafting reaction efficiency is too low.

[0072] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for modifying the interface enhanced insulation of a two-component liquid silicone rubber cable accessory, characterized in that: include: (1) Preforming two-component liquid silicone rubber to obtain a preformed cable accessory sample; The operation process of (1) is as follows: after fully mixing the component A and the component B constituting the two-component liquid silicone rubber, injecting them into the mold of the cable accessory, pressurizing and heating them, and obtaining a preformed two-component liquid silicone rubber cable accessory sample; Component A includes vinyl rubber and platinum catalyst; component B includes vinyl rubber and hydrogen-containing silicone oil; The conditions of pressurized heating treatment are: temperature 90-120°C, pressure 10-15MPa, time 8-15min; (2) Spray the heated and melted graftable compound onto the surface of the cable accessory sample, and apply pressure to the surface using a mold at a temperature above the melting point of the graftable compound to form a uniform liquid film of the graftable compound. After the pressure is applied for a certain period of time, the entire surface is subjected to a vulcanization grafting treatment; The graftable compound is 4-propyleneoxy-2-hydroxybenzophenone; (3) After the vulcanization treatment is completed, the mold is removed, the modified surface is rinsed with a solvent, and then dried to complete the interface insulation modification of the two-component liquid silicone rubber cable accessories.

2. The method according to claim 1, characterized in that (2) The middle mold applies pressure to the sample surface for 10-60 minutes at a pressure of 300-600 Pa.

3. The method according to claim 1, characterized in that (2) The temperature of the vulcanization grafting treatment is 180-220°C and the time is 3-8h.

4. The method according to claim 1, characterized in that: (2) The spraying amount of the grafted compound is 1-2 g / dm 2 .

5. The method according to claim 1, characterized in that (2) The middle mold is made of inorganic glass or ceramic.

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